The present invention relates to a reversibly discoloring composition capable of reversibly changing color according to the wavelength of an external light source and a member using the composition used as external decorating parts of dial plates, bands, etc., for wrist watches, and has a feature that the object color of the member reversibly and instantly changes color according to the wavelength of an external light source.
Heretofore, as a substance characterized in that the color of the compound undergoes reversible discoloring by light irradiation, a photochromic molecule is known. By absorbing the energy of light irradiation, the photochromic molecule changes chemical structure and as the result thereof, the color of the compound is changed. As the photochromic molecule, spiropyran, in which the object color changes from colorless to blue-purple or red-purple by an ion dissociation, thioindigo, in which the object color changes from a purple color to a red color by a trans-cis isomerization, fulgide and dihydropyrene, in which the object color changes from colorless to a pink color by an electrocyclic reaction, triphenylimidazolyl, in which the object color changes by a radical dissociation, a thionine-base photochromic molecule, in which the object color changes by oxidation reduction, etc., are known. An example of using a photochromic molecule as a coloring material, that is a light-discoloring ink, is disclosed in U.S. Pat. No. 5,028,792 (WO 94/23062). As other uses than the above-described uses, dyeing is applied to a part of a clothing ornament using a photochromic molecule as a dye and a clothing ornament causing color changing in the portion, etc., is known.
However, in the case of using such a photochromic molecule as a coloring material, there are many cases that the reversibility of the color change is imperfect and the time required for color changing is long. Also, when the change of color by the absorption of light is repeatedly carried out, a photo-deterioration such as vanishing of reversibility of color change, etc., occurs, and further, by heat or the ultraviolet irradiation of a long time, the reversibility of color change is frequently vanished, and the photochromic molecule is not suitable for the storage for a long period of time. As described above, when the photochromic molecule of prior art is used as an external decorating part for watch, it sometimes difficult to ensure the satisfactory quality. Also, because the color change depends upon the chemical structure, the color can be changed only between colorless and one color or between two colors.
The present invention has been made in view of such circumstances and the problems of the invention are to supply easily and at a low cost an external decorating part for a watch using a member that the object color is instantly and reversibly changes according to the kind of a light source and further to ensure the quality such as the light resistance, the heat resistance, etc.
The reversibly discoloring composition of the invention for solving the problems is composed of fine particles made of one or more kinds of rare earth oxides represented by a formula M2O3 (wherein M represents Ho, Nd, or Pr) and a light-transmitting base material having dispersed therein the fine particles.
In this case, in the rare earth oxide fine particles in the invention, the mean particle size is from about a few xcexcm to 100 xcexcm but it is preferred to use super fine particles having the means particle size of from 5 nm to 100 nm. When such super fine particles are used, the characteristics that the change of the color tone is large and dispersibility is good are shown and even by using the same rare earth oxide, a reversibly discoloring layer having a different color tone can be formed. In addition, the fine particles having different mean particle size may be mixed, whereby the variation of expressible colors can be increased. In addition, the fine particles having different mean particle size may be mixed, whereby the variation of expressible colors can be increased.
The light-transmitting base material in the invention includes, for example, inks or coating materials selected from an epoxymelamine-base high molecular material, a vinyl-base high molecular material, an acrylic high molecular material, a urethane-base high molecular material, a polyamide-base high molecular material, an alkid-base high molecular material, a photo-setting type high molecular material, and a high molecular material having a light transmittance. In this case, the material having a light transmittance means that the visible light transmittance of the material is at least 90%.
Also, the light-transmitting base material of the invention includes, for example, a molding material selected from an acrylic high molecular material, a polycarbonate high molecular material, an ABS high molecular material, a polyarylate high molecular material, a urethane-base high molecular material, a styrene-base high molecular material, a silicone-base high molecular material, and a high molecular material having a light transmittance. In this case, the material having a light transmittance means that the visible light transmittance of the material is at least 90%.
In the present invention, to 100 parts by weight of the light-transmitting base material, from 1 to 30 parts by weight of the rare earth oxide fine particles can be used but particularly, when the light-transmitting base material is a base material for ink, to 100 parts by weight of the base material, the rare earth oxide fine particles can be used in the range of from 1 to 50 parts by weight.
Also, to improve the dispersibility, if necessary, additives such as a wetting agent, etc., may be added.
The reversibly discoloring composition of the invention can be used for various kinds of uses but particularly, is suitably used as external decorating parts for watches, such as a dial plate, a frame, a band, a bezel, a button, etc., for watches. That is, the external decorating part for watch of the invention has the color changing portion composed of a light-transmitting base material having dispersed therein fine particles of one or more kinds of rare earth oxides represented by the formula M2O3 (wherein M represents Ho, Nd, or Pr).
In this case, the rare earth oxide fine particles and the light-transmitting base material are as described above, but according to the kind of the light-transmitting base material, the forming method of the color changing portion differs.
For example, the color changing portion is formed by printing or coating a transparent ink or a transparent coating material containing the rare earth oxide fine particles or formed by molding a transparent molding material containing the rare earth oxide fine particles. Practically, a high molecular material layer containing the rare earth oxide fine particles is formed in an optional form by printing b such as screen printing, etc., or coating on a dial plate, etc., which is an external decorating part for a watch. Also, it is possible that after dispersing a proper amount of the rare above-described earth oxide fine particles in a transparent resin such as a polycarbonate resin, a urethane resin, etc., pellets are formed from the dispersion, and thereafter, by applying a molding work such as injection molding, etc., the pellets are molded to a desired form, which is used as an external decorating part for a watch or a member of the external decorating part for a watch.
The color changing portion thus formed changes the color thereof reversibly and instantly according to the kind of an external light source such as sunlight, an ordinary type fluorescent lamp, a three-wavelength region light-emitting type fluorescent lamp, etc.
Such a color changing portion may be used as a part of the member or may be used as the whole portion. Also, the color changing portion may be covered with the transparent layer or member made of a light-transmitting material. In this case, at the surrounding of the color changing portion may be formed color members of almost the same color as the changed color formed by the color changing portion by the light of a specific external light source.
The rare earth oxide contained in the reversibly discoloring composition of the invention has the feature in the reflected spectral distribution. That is, the rare earth oxide has plural absorption peaks in a visible light region. These absorption peaks are caused by the absorption of the ion of the rare earth element M contained in the oxide shown by the above-described formula M2O3 and the diffractionxc2x7scattering by the fine particles. As an example,f the diffusion reflection spectral characteristics of Ho2O3 having a mean particle size of about 2 xcexcm are shown in FIG. 1.
As shown in FIG. 1, Ho2O3 has the principal absorption peaks near 460 nm, 540 nm, and 650 nm. On the other hand, sunlight, which becomes an external light source, has a light of wavelengths from a ultraviolet region to an infrared region and when Ho2O3 is irradiated by the sunlight, the spectral distribution showing the object color causes absorptions of the wavelengths of near 460 nm, 540 nm, and 650 nm, and the light of other wavelengths is reflected at the reflectance of FIG. 1. As the result thereof, the object color shows a light yellow color. Then, as an example of the external light source, an example of the spectral distribution of a high color rendering type fluorescent lamp or an ordinary type (high-efficient type) fluorescent lamp is shown in FIG. 2 (ordinary type white fluorescent lamp manufactured by TOSHIBA LIGHTING and TECHNOLOGY CORPORATION, cited from a Toshiba lamp catalogue). When Ho2O3 is irradiated by the fluorescent lamp as an external light source, the wavelengths of near 460 nm, 540 nm, and 650 nm are absorbed, and the light of other wavelengths is reflected at the reflectance of FIG. 1. Because the light emission intensity of each wavelength is low as compared with sunlight, the reflected light intensity in each wavelength is different from the case of sunlight, and as the result thereof, the object color of Ho2O3 shows the color of from a white color to a light flesh color. The width of color changing is caused by the difference of the deflection spectral distribution according to the kind of a fluorescent lamp.
Then, the spectral distribution of the three-wavelength region light-emitting type fluorescent lamp is shown in FIG. 3 (Melo 5 N manufactured by TOSHIBA LIGHTING and TECHNOLOGY CORPORATION, cited from a Toshiba lamp catalogue). As shown in FIG. 3, the three-wavelength region light-emitting type fluorescent lamp has large emission lines near 490 nm, 550 nm, and 620 nm. When Ho2O3 is irradiated by the three-wavelength region light-emitting type fluorescent lamp as an external light source, because of the reflection spectral characteristics shown in FIG. 1, the light near 490 nm contained in the fluorescent lamp is almost absorbed and although the wavelengths near 550 may be reflected to some extent, the light emission intensity becomes low. Also, only the light of the wavelength of 620 nm is intensely reflected. As the results thereof, the object color of Ho2O3 shows the color of from a light orange color to a flesh color by the wavelength of 550 nm having a low light emission intensity and the wavelength of 620 nm having a high light emission intensity. The width of color changing is caused by the difference of the kind of the three-wavelength region light-emitting type fluorescent lamp.
Also, it is known that. the light emission intensity of Ho2O3 is not intense but when the oxide absorbs a light of specific wavelengths of blue and green, it emits a red color and it is considered that the light emission of a red color causing in the case of being irradiated by a light of a specific wavelength, that is the light emitting phenomenon contributes to that the subject color is seen as a color of from a light orange color to a flesh color. As described above, by mixing the above-described rare earth oxide in a transparent resin component and applying shaping such as printing, etc., to an external decorating part for a watch, which is exposed to an external light source, the part can show a subject color corresponding to the kind of the external light source and as the result thereof, an expression which has never been obtained can be easily applied to the external part of watch at a low cost. Also, because the fine particles constituting the above-described color changing layer are the oxide, the layer is excellent in the qualities such as the light resistance, the heat resistance, etc., and because the layer is not accompanied by the change of the chemical structure as a photochromic molecule, even when the subject color is repeatedly changed by changing an external light source, the functional property thereof is not spoiled and the color change occurs instantly.
Also, in such rare earth oxide fine particles, particularly, the super fine particles of a nanometer order have a different reflection spectral characteristics from the above-described rare earth oxide fine particles of a micrometer order. As an example, the reflection spectral characteristics of Ho2O3 fine particles having a mean particle size of about 2 xcexcm and the reflection spectral characteristics of Ho2O3 super fine particles having a mean particle size of about 30 nm are shown in FIG. 4. As shown in FIG. 4, Ho2O3 has the principal absorption peaks near 460 nm, 540 nm, and 650 nm regardless of the particle sizes but the reflectance is lower in the super fine particles, and in particular, the reflectance largely differs in the absorption regions near 540 nm and 650 nm.
As the result thereof, when the rare earth oxide fine particles are exposed to the three-wavelength region light-emitting type fluorescent lamp having large emission lines near 490 nm, 550 nm, and 620 nm, because in the case of the Ho2O3 super fine particles, the light of the wavelengths of bear 540 nm and 650 nm is large absorbed, and the emission line near 620 nm contained in the three-wavelength region light-emitting type fluorescent lamp is reflected, the color tone of the Ho2O3 super fine particles becomes a strong red color and as the result thereof, the subject color becomes a deep pink color. By mixing the above-described rare earth oxide super fine particles in the transparent resin component and applying shaping such as printing, etc., to an external decorating part for a watch, which is exposed to an external light source, the color tone largely changes according to the kind of the external light source and it becomes possible to express a color which has never been obtained.
Also, because such super fine particles have a small surface area, the dispersibility thereof in the case of mixing in a light-transmitting base material such as a transparent high molecular material, etc., is good, and further in the case of applying a screen printing work, a screen plate having a fine mesh size can be used. Also, because the super fine particles are same as the fine particles of a micrometer order in the point of being an oxide, the rare earth super fine particles are excellent in the qualities such as the light resistance, the heat resistance, etc., and because the particles are not accompanied by the change of the chemical structure as in the case of a photochromic molecule, even when the subject color is repeatedly changed by changing an external light source, the functional property is not spoiled and the color occurs instantly.